<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <title>基本规范</title>
    <style>
        body {
            margin: 0;
            overflow: hidden;
        }

        #canvas {
            background-color: antiquewhite;
        }
    </style>
</head>

<body>
<canvas id="canvas"></canvas>
<!-- 顶点着色器 -->
<script id="vertexShader" type="x-shader/x-vertex">
    void main(){
      //点位
      gl_Position=vec4(0,0,0,1);
      //尺寸
      gl_PointSize=512.0;
    }
  </script>
<!-- 片元着色器 -->
<script id="fragmentShader" type="x-shader/x-fragment">
    precision mediump float;
    //向量加法
    /*
      向量加法
    */
    vec4 v=vec4(1,2,3,4)+vec4(5,6,7,8);
    void main(){
      gl_FragColor=v/255.0;
    }
  </script>
<script type="module">
  import { initShaders } from "../jsm/Utils.js";

  const canvas = document.querySelector("#canvas");
  canvas.width = window.innerWidth;
  canvas.height = window.innerHeight;

  // 获取着色器文本
  const vsSource = document.querySelector("#vertexShader").innerText;
  const fsSource = document.querySelector("#fragmentShader").innerText;

  //三维画笔
  const gl = canvas.getContext("webgl");

  //初始化着色器
  //功能：解析着色器文本，整合到程序对象里，关联webgl上下文对象，实现两种语言的相互通信
  initShaders(gl, vsSource, fsSource);

  //声明颜色 rgba
  gl.clearColor(0, 0, 0, 1);
  //刷底色
  gl.clear(gl.COLOR_BUFFER_BIT);

  //绘制顶点
  gl.drawArrays(gl.POINTS, 0, 1);

  //像素容器
  const pixel = new Uint8Array(4)
  //抓取像素
  gl.readPixels(
    canvas.width / 2, canvas.height / 2,
    1, 1,
    gl.RGBA,
    gl.UNSIGNED_BYTE,
    pixel
  )

  console.log(pixel);
</script>
</body>

</html>
